RF design - simple question - RF Cafe Forums

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matrixrf
 Post subject: RF design - simple question
Posted: Wed Mar 07, 2007 3:50 pm 
 
Lieutenant

Joined: Wed Mar 07, 2007 3:42 pm
Posts: 1
What effect does return loss have on Transmit Power?
Is it a one to one correlation?

eg. Tx power is 30 dB
RL = -12 dB

What is actually transmitted?

Thanks
 
   
 
Kirt Blattenberger
 Post subject:
Posted: Wed Mar 07, 2007 5:53 pm 
 
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 676
Location: Erie, PA
Greetings matrixrf:

Return loss is the relative power of the reflected part of the signal, and the remaining power gets through to the antenna. For your case, the reflected signal is 30 dBm - 12 dB = 18 dBm. To get the final transmitted power number, you need to convert those powers to watts, subtract, then convert back to a dBm value.

30 dBm = 1000 mW (incident power)
18 dBm = 63.1 mW (reflected power)

(1000 - 63.1) mW = 936.9 mW (transmitted power)
936.9 mW = 29.7 dBm

For dBm <--> mW conversion see here:

http://www.rfcafe.com/references/electrical/mw2dbm.htm

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- Kirt Blattenberger :smt024
RF Cafe Progenitor & Webmaster




Posted  11/12/2012